Manninen, S. | bioRxiv Science

bioRxiv2022

Endogenous opioid release following orgasm in man: A combined PET-fMRI study

Sex is one of the most rewarding and motivating behaviours for humans. Endogenous mu-opioid receptor system (MORs) plays a key role in the mammalian reward circuit. Both human and animal experiments suggest the involvements of MORs in human sexual pleasure, yet this hypothesis currently lacks in vivo support. We used positron emission tomography (PET) with the radioligand [11C]carfentanil, which has high affinity for MORs to quantify endogenous opioid release following orgasm in man. Subjects were scanned twice: Once immediately after reaching an orgasm and once in a baseline state. Haemodynamic activity was measured with functional magnetic resonance imaging during penile stimulation from partner. The PET data revealed significant opioid release in hippocampus. Haemodynamic activity in somatosensory and motor cortices as well as hippocampus and thalamus increased during penile stimulation, and thalamic activation was linearly dependent on self-reported sexual arousal. Altogether these data show that endogenous opioidergic activation in the medial temporal lobe is centrally involved in sexual arousal.

neuroscience↗

bioRxiv2020

Cerebral grey matter density is associated with neuroreceptor and neurotransporter availability: A combined PET and MRI study

Positron emission tomography (PET) can be used for in vivo measurement of specific neuroreceptors and transporters using radioligands, while voxel-based morphometric analysis of magnetic resonance images allows automated estimation of local grey matter densities. However, it is not known how regional neuroreceptor or transporter densities are reflected in grey matter densities. Here, we analyzed brain scans retrospectively from 325 subjects and compared grey matter density estimates with three different neuroreceptors and transporter availabilities. {micro}-opioid receptors (MORs) were measured with [11C]carfentanil (162 scans), dopamine D2 receptors with [11C]raclopride (91 scans) and serotonin transporters (SERT) with [11C]MADAM (72 scans). The PET data were modelled with simplified reference tissue model. Voxel-wise correlations between binding potential and grey matter density images were computed. Regional binding of all the used radiotracers was associated with grey matter density in region and ligand-specific manner independently of subjects age or sex. These data show that grey matter density and MOR and D2R neuroreceptor / SERT availability are correlated, with effect sizes (r2) ranging from 0.04 to 0.69. This suggests that future studies comparing PET outcome measure different groups (such as patients and controls) should take grey matter density differences between the groups into account.

neuroscience↗